"I doubt Americans want the government to decide when life is worth preserving and when life can be destroyed," says Sen. Sam Brownback. That's why the Kansas Republican wants to insert the federal government into deeply personal end-of-life decisions, prohibiting doctors from helping terminally ill patients choose the time and manner of their deaths.

Brownback says assisting suicide is not, properly speaking, a medical function, and I agree. But Congress has made it a medical function by requiring a doctor's prescription to obtain the drugs that are best suited for the purpose. Brownback's recently introduced Assisted Suicide Prevention Act, if effective, would force patients to preserve lives they do not consider worth preserving or to use messier, less reliable, more painful methods.

So far Oregon is the only state that allows doctors to prescribe drugs for suicide. In January the U.S. Supreme Court ruled that Oregon's assisted suicide law does not conflict with the federal Controlled Substances Act. Brownback's bill would amend the act to revoke the prescribing privileges of doctors who help patients obtain lethal doses of controlled substances, thereby nullifying Oregon's law.

Like Brownback, I'm not a big fan of Oregon's Death With Dignity Act. To my mind, it unduly restricts individual freedom and misleadingly medicalizes a moral decision. But it does give patients an option they would not otherwise have, and it's the sort of state policy experiment our Constitution requires the federal government to allow.

Under Oregon's law, a patient can obtain a prescription for barbiturates (the lethal agent of choice) only if he's expected to live six months or less, his diagnosis and prognosis are confirmed by a second physician and he makes two oral requests separated by at least 15 days, followed by a written request signed in the presence of two witnesses. He may also have to undergo a psychological examination to show his judgment is not impaired.

The Death With Dignity Act has been in force for nearly a decade now, and it has not precipitated a mad rush for the exit it unlocked. Last year 38 patients used drugs prescribed under the law to kill themselves, almost the same as the 2004 total and down from a peak of 42 in 2003. Close to half of the patients who use the law to get barbiturate prescriptions do not take the drugs, but presumably they derive comfort from having the option.

Brownback and other critics of physician-assisted suicide imagine that this highly constrained experiment in expanded autonomy for people on the verge of death will somehow devolve into a homicidal free-for-all featuring involuntary euthanasia and infanticide. This is like assuming that allowing women to get breast implants will lead plastic surgeons to start kidnapping those they deem insufficiently endowed and cutting into them without permission.

The main cautionary example cited by opponents of Oregon's law is the Netherlands, where doctors do not merely assist suicide but directly kill patients, sometimes without their consent. The most striking feature of the Dutch approach, as described by its critics, is that the rules, including the crucial condition of patient consent, are neither followed nor enforced. Whatever may be said for the Dutch pragmatism that, say, tolerates the retail sale of marijuana even though it's officially illegal, the distinction between suicide and homicide is an area where following the law should not be optional.

Instead of drawing clear lines, Brownback's bill would push doctors into a gray zone beyond the law. His ban is ostensibly limited to prescriptions "for the stated or undisputed purpose of assisting suicide," a restriction meant to protect doctors who prescribe narcotic painkillers that may incidentally hasten death by depressing respiration. If this safeguard is as strong as Brownback claims, doctors could always prescribe large doses of narcotics with a wink and a nod to patients who wanted to kill themselves. The upshot would be more lies, not fewer suicides.